Antenna device having a band pass filter

ABSTRACT

In order to perform feeding to an inverted F antenna having a plate conductor of an approximately rectangular shape for forming a radiation conductor and a ground conductor arranged in parallel with the plate conductor, a strip conductor plate connected to a feeder line is provided on the ground conductor via a dielectric substrate. Hence, the feeding from the feeder line to the inverted F antenna 37 is performed by an electric field coupling of the plate conductor and the strip conductor plate. The inverted F antenna and a resonator are integrated by coupling means to carry out an impedance matching, and the inverted F antenna and the resonator 62 constitute a band pass filter.

This application is a continuation of application Ser. No. 07/930,544filed Nov. 23, 1992, now Pat. No. 5,434,579 issued Jul. 18, 1995.

TECHNICAL FIELD

The present invention relates to an antenna device, and moreparticularly to a structure for feeding to an antenna device of a platestructure, mainly used in a VHF band, a UHF band and a microwave band,and an improvement of a filter used therefor.

BACKGROUND ART

FIG. 10 shows a conventional antenna device, for example, as disclosedin "Inverted F-shaped Antenna for Portable Radios", Hiroshi HARUKI etal., No. 613 of 1982 Overall Annual Conference of the Institute ofElectronics and Communication Engineers of Japan.

In FIG. 10, the conventional inverted F antenna 17 includes a plateconductor 11 with an approximately rectangular shape constituting aradiative conductor, and a ground conductor 12 constituted by metallicplates of a radio frame body. The plate conductor 11 is arrangedapproximately in parallel with the ground conductor 12, and one end inits longitudinal direction is connected to the ground conductor 12 by agrounding conductor 13. A coaxial line 14 as a feeder line for theantenna 17 is comprised of an internal conductor 15 and an externalconductor 16.

The internal conductor 15 of the coaxial line 14 is directly connectedto the facing surface of the plate conductor 11 in a position close tothe grounding conductor 13 by soldering or the like. The externalconductor 16 of the coaxial line 14 is connected to the ground conductor12.

Next, the operation of the conventional inverted F antenna 17 will nowbe described.

In the inverted F antenna 17, the plate conductor 11 and the groundconductor 12 constitute a parallel flat line, and, since one end in thelongitudinal direction of the plate conductor 11 is a short-circuit endand the other end is an open end, the inverted F antenna 17 resonateswith an electric wave with a particular frequency f_(o) depending on thelongitudinal length of the plate conductor 11. Hence, the inverted Fantenna 17 shown in FIG. 10 acts as a resonator with one short-circuitend and the other open end and possesses a function of an antennadevice. Accordingly, a radio wave with a frequency f_(o) fed to theinverted F antenna 17 via the internal conductor 15 of the coaxial line14 is resonated by the inverted F antenna 17 to be radiated externally.In this case, the impedance matching of the coaxial line 14 with theinverted F antenna 17 is controlled by the connection position of theinternal conductor 15 with the plate conductor 11.

Conventionally, since an antenna device of this kind is constructed bydirectly connecting the conductor to the inverted F antenna 17, asdescribed above, in order to connect the internal conductor 15 with theplate conductor 11, it is necessary to carry out a soldering operationon the facing surface of the plate conductor 11 to the ground conductor12 or to provide a through-hole in the plate conductor 11 and thesoldering thereon, and thus it is troublesome to manufacture it.

Further, since the impedance matching of the input impedance of theinverted F antenna 17 to the characteristic impedance of the coaxialline 14 is controlled by the connection position of the internalconductor 15 with the plate conductor 11, in order to perform theimpedance matching, the connection position of the internal conductor 15with the plate conductor 11 is unequivocally determined. Hence, therestriction arises in arranging the parts, and the wiring of the coaxialline 14 becomes difficult.

FIG. 11 shows a conventional filter antenna device, as disclosed in "RFBranching System for the Amps Mobile Telephone Equipment", I. YOSHIDA etal., 29th IEEE Vehicular Technology Conference IEEE Catalog No. 79 CH1378-9 VT, pp. 178-180, 1979. In FIG. 11, an antenna 20 is connected toa band pass filter 22 through a connection cable 24 and connectors 26.

In this case, since the band pass filter 22 is designed so as usually topass a wave of only a transmission and receiving frequency band, whenthe antenna device using this conventional filter is used for receiving,the wave within the receiving frequency band received by the antenna 20is passed through the band pass filter 22 to input to a receiver.However, an unwanted wave outside the receiving frequency band isstopped by the band pass filter 22 and can not be input to the receiver.On the other hand, when the antenna device using this conventionalfilter is used for transmitting, only the wave within the transmissionfrequency band is led from the antenna 20 and the unwanted wave outsidethe transmission frequency band is stopped by the band pass filter 22.Hence, only the wave within the transmission frequency band can beemitted from the antenna 20.

As described above, the antenna device using the filter 22, as shown inFIG. 11, has a function to receive or transmit only the wave within thenecessary frequency band.

However, in the conventional antenna device having the structuredescribed above, the connection cable 24 and the connectors 26 forconnecting the antenna 20 with the band pass filter 22 are required.Thus, the device is enlarged and the loss is increased. Further, sincethe antenna 20 and the band pass filter 22 independently function oroperate, it is necessary to provide a matching portion for performingthe impedance matching of the antenna 20, and the antenna 20 isenlarged. Also, since the antenna 20 constitutes a one stage resonator,it is difficult to perform the impedance matching over a wide band.

In the conventional antenna device, when the inverted F antenna 17 isused as the antenna 20, these problems of the necessity of the matchingportion provision and the difficulty of the wide band impedance matchingbecome particularly troublesome.

DISCLOSURE OF INVENTION

The present invention is achieved in order to prevent theabove-described problems of the prior art, and it is a first object ofthe present invention to provide an antenna device capable of readilyperforming a feeding to an inverted F antenna.

At the same time, it is a second object of the present invention toprovide an antenna device capable of performing with a small size, a lowloss and over a wide band, being particularly suitable for an inverted Fantenna.

In order to solve the aforementioned problems, in an antenna deviceaccording to the present invention, an electrode for performing anelectric field or magnetic field coupling is provided to a plateconductor, and by the electric field or magnetic field coupling of theelectrode and the plate conductor, a non-contact feeding from a feederline to an antenna can be performed.

Further, a resonant element is also provided, and by integrating theresonant element and the plate conductor to constitute a filter, animpedance matching of the antenna device can be carried out over a wideband.

In a more specific description of the structure of the presentinvention, in order to achieve the first object, the antenna deviceaccording to the present invention comprises a first conductor plate forforming a radiation conductor of an antenna; a second conductor platearranged approximately in parallel with the first conductor plate forforming a ground conductor of the antenna; a conductor for connectingthe first conductor plate with the second conductor plate at one end ofthe first conductor plate; a feeder line; and a third conductor platefor feeding, which is arranged between the first conductor plate and thesecond conductor plate and is connected to the feeder line to causeeither an electric field or magnetic field coupling between the firstconductor plate and the third conductor plate.

In the antenna device according to the present invention, as constructeddescribed above, since between a first conductor plate for forming aradiation conductor of an antenna and a second conductor plate forforming a ground conductor of the antenna, a third conductor plateconnected to a feeder line is inserted in a position for causing anelectric field or magnetic field coupling between the first conductorplate and the third conductor plate, the electric field or magneticfield coupling is caused, and thus a non-contact feeding from the feederline to the antenna can be carried out. Also, by varying the intervalbetween the first conductor plate and the third conductor plate or thedimension of the third conductor plate, the coupling amount iscontrolled. Further, since an impedance matching of the feeder line andthe antenna is obtained, the arrangement restriction of the firstconductor plate and the feeder line can be relieved.

Further, in order to achieve the second object, an antenna deviceaccording to the present invention comprises an antenna constituted by aresonant element such as a dipole antenna, an inverted F antenna, apatch antenna or the like, a resonator and a coupling means for couplingthe antenna with the resonator, the coupling means integrating theantenna and the resonator to perform an impedance matching, the resonantelement and the resonator constituting a band pass filter.

In the antenna device according to the present invention, as constructeddescribed above, since the resonant element of the antenna acts as theresonator of the last stage in the band pass filter, the housing of theresonators can be reduced by one stage, and the antenna device can beminiaturized with a low loss. Also, since the antenna and the resonatorsare integrated to perform the impedance matching, no individual matchingportion is required to the antenna, and thus a small-sized antennadevice can be obtained. Further, by integrating the antenna and theresonators, a multi-stage filter including the antenna can be obtained,and thus the impedance matching over the wide band can be carried out.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an essential part of a first embodimentof an antenna device according to the present invention;

FIG. 2 is a cross section, taken along the line A--A of the antennadevice shown in FIG. 1;

FIG. 3 is a perspective view of an essential part of a second embodimentof an antenna device according to the present invention;

FIG. 4 is a perspective view of an essential part of a third embodimentof an antenna device according to the present invention;

FIG. 5 is a perspective view of an essential part of a fourth embodimentof an antenna device according to the present invention;

FIG. 6 is a perspective view of an essential part of a fifth embodimentof an antenna device according to the present invention;

FIG. 7 is a block diagram showing a structure of a filter for use in anantenna device according to the present invention;

FIG. 8 is a perspective view of an essential part of a sixth embodimentof an antenna device according to the present invention;

FIG. 9 is a perspective view of an essential part of a seventhembodiment of an antenna device according to the present invention;

FIG. 10 is a schematic perspective view of a conventional antennadevice; and

FIG. 11 is a block diagram showing a structure of a filter for use in aconventional antenna device.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 is a perspective view showing an essential part of one preferredembodiment of an antenna device according to the present invention. Theone preferred embodiment of the antenna device according to the presentinvention is constructed as an inverted F antenna 37 provided with afeeding means.

In FIG. 1, the inverted F antenna 37 includes a plate conductor 31 withan approximately rectangular shape constituting a radiative conductor,and a ground conductor 32 constituted by metallic plates of a radioframe body. The plate conductor 31 is arranged approximately in parallelwith the ground conductor 32, and one end in the longitudinal directionof the plate conductor 31 is connected to the ground conductor 32 by agrounding conductor 33. A coaxial line 34 as a feeder line for theinverted F antenna 37 is comprised of an internal conductor 35 and anexternal conductor 36.

In this embodiment, as a distinctive feature, a dielectric substrate 38provided with a third conductor plate 39 therein is mounted on theground conductor 32, and the third conductor plate 39 is connected withthe internal conductor 35 of the coaxial line 34, as hereinafterdescribed in detail. Hence, a non-contact feeding can be performed tothe inverted F antenna 37 from the coaxial line 34 as the feeder line.

In FIG. 1, the third conductor plate is shown as a strip conductor 39and is formed on the surface of the dielectric substrate 38. The stripconductor 39 as the third conductor plate is arranged facing the plateconductor 31 between the plate conductor 31 and the ground conductor 32.Further, in this embodiment, the ground conductor 32, the dielectricsubstrate 38 and the strip conductor 39 constitute a micro strip line40. In this case, the strip conductor 39 is coupled with the internalconductor 35 at one end on an opening side of the plate conductor 31,and the other end is an open end.

Next, the operation of the antenna device described above will now bedescribed.

In the above-described antenna device, in a similar manner to theconventional antenna device described previously, the inverted F antenna37 acts as a resonator with one short-circuit end and the other open endat a particular frequency f_(o) depending on the longitudinal length ofthe plate conductor 31.

FIG. 2 is a cross section, taken along the line A--A shown in FIG. 1 forthe explanation of the feeding in the above-described antenna device. InFIG. 2, the same numerals denote the same parts as those shown in FIG.1.

In the drawings, when an electric wave having a frequency f_(o) istransmitted to the micro strip line 40 from the coaxial line 34, anelectric field as shown by arrows in FIG. 2 is caused between the plateconductor 31 and the strip conductor 39, and thus an electric fieldcoupling between the micro strip line 40 and the inverted F antenna 37is mainly carried out. Hence, a non-contact feeding of the wave of thefrequency f_(o) is performed to the inverted F antenna 37 from thecoaxial line 34 by the electric field coupling. The fed wave of thefrequency f_(o) is resonated by the inverted F antenna 37 and is emittedexternally from the same.

As described above, in the inverted F antenna 37 shown in FIG. 1, havinga function of an antenna device, the impedance matching between thecoaxial line 34 and the inverted F antenna 37 can be controlled byvarying the position and the dimension of the strip conductor 39 withrespect to the plate conductor 31 or the interval between the plateconductor 31 and the strip conductor 39.

Further, in this embodiment shown in FIG. 1, since the open ends of theplate conductor 31 and the strip conductor 39 face in mutually oppositedirections and thus the current flows on the opposite surfaces of theplate conductor 31 and the strip conductor 39 are in oppositedirections, a potential difference therebetween becomes large and aclose coupling due to the electric field can be readily obtained. Also,even when the position of the micro strip line 40 is varied, by varyingthe size of the strip conductor 39 or the interval between the plateconductor 31 and the strip conductor 39, the impedance matching can bereadily controlled.

FIG. 3 is a perspective view showing an essential part of the secondembodiment of an antenna device according to the present invention. InFIG. 3, the same numerals denote the same parts as those of the firstembodiment shown in FIG. 1 and thus the description thereof can beomitted for brevity.

In the second embodiment, as a distinctive feature, the open end of thestrip conductor 39 is arranged on the opposite side to the firstembodiment, that is, the open end of the strip conductor 39 is arrangedon the opening side of the plate conductor 31. The other end of thestrip conductor 39 is coupled with the internal conductor 35 of thecoaxial line 34.

Next, the operation of the antenna device described above will now bedescribed.

In this case, the basic operation of the above-described secondembodiment is the same as the first embodiment shown in FIG. 1. That is,when the electric wave having the frequency f_(o) is transmitted to themicro strip line 40 from the coaxial line 34, the electric field asshown by the arrows in FIG. 2 is caused between the plate conductor 31and the strip conductor 39, and thus the electric field coupling betweenthe micro strip line 40 and the inverted F antenna 37 is mainly carriedout. Hence, the non-contact feeding of the wave of the frequency f_(o)is performed to the inverted F antenna 37 from the coaxial line 34 bythe electric field coupling. The fed wave of the frequency f_(o) isresonated by the inverted F antenna 37 and is emitted externally fromthe same.

In the above-described embodiment, since the open ends of the plateconductor 31 and the strip conductor 39 face the same direction and thusthe current flows on the opposite surfaces of the plate conductor 31 andthe strip conductor 39 are in the same direction, the potentialdifference becomes small and a loose coupling due to the electric fieldcan be readily obtained. In this case, since the current flow directionsare the same, a magnetic field coupling becomes strong.

FIG. 4 is a perspective view showing an essential part of the thirdembodiment of an antenna device according to the present invention. InFIG. 4, the same numerals denote the same parts as those of the firstembodiment shown in FIG. 1 and thus the description thereof can beomitted for brevity.

In the third embodiment, as a distinctive feature, a conductor block 41is provided. That is, the conductor block 41 is inserted between theplate conductor 31 and the ground conductor 32 and is contacted with theground conductor 32 at one surface and with the dielectric substrate 38at the other surface. Hence, the dielectric substrate 38 is mounted onthe conductor block 41, and the strip conductor 39 facing the plateconductor 31 is attached onto the dielectric substrate 38.

In the third embodiment, by properly determining the thickness of theconductor block 41, the interval between the plate conductor 31 and theconductor block 41 can be narrowed compared with the interval betweenthe plate conductor 31 and the ground conductor 32. Also, since anelectrostatic capacity is caused between the plate conductor 31 and theconductor block 41, a resonance frequency can be controlled by thiselectrostatic capacity and the plate conductor 31 can be effectivelyminiaturized. Further, by varying the area of the conductor block 41,the electrostatic capacity between the plate conductor 31 and theconductor block 41 can also be changed.

Further, in the above-described third embodiment, the feeding operationdescribed in the first and second embodiments can be applied, and thus,by similarly operating, the same effect can be obtained.

FIG. 5 is a perspective view showing an essential part of the fourthembodiment of an antenna device according to the present invention. InFIG. 5, the same numerals denote the same parts as those of the firstembodiment shown in FIG. 1 and thus the description thereof can beomitted for brevity.

In the fourth embodiment, as a distinctive feature, a filter 42 is usedin place of the conductor block 41 in the third embodiment.

In this case, the filter 42 includes an input terminal 43 and an outputterminal 44, and a connection conductor 45 couples the output terminal44 with the strip conductor 39.

In this embodiment, the filter 42 has an external shape of anapproximately rectangle, and almost all surroundings of the filter 42except a small part are covered by a conductor. The input terminal 43and the coaxial line 34 are connected to each other by the internalconductor 35. The output terminal 44 and the strip conductor 39 arecoupled with each other by the connection conductor 45. Although theexample of the filter 42 having the external form of the approxi-matelyrectangle has been shown, this is for handling convenience and thus thisembodiment is not restricted to this form.

In this embodiment, since the electrostatic capacity is caused betweenthe plate conductor 31 and the filter 42 in the same manner as theembodiment shown in FIG. 4, a resonance frequency can be controlled bythe electrostatic capacity and the plate conductor 31 can be effectivelyminiaturized. Further, the filter 42 is inserted between the plateconductor 31 and the ground conductor 32, and hence the antenna devicecan be miniaturized.

Further, in the above-described fourth embodiment, the feeding shown inthe first and. second embodiments can be applied, and thus, by similarlyoperating, the same effect can be obtained.

FIG. 6 is a perspective view showing an essential part of the fifthembodiment of an antenna device according to the present invention. InFIG. 6, the same numerals denote the same parts as those of the firstembodiment shown in FIG. 1 and thus the description thereof can beomitted for brevity.

In the fifth embodiment, as a distinctive feature, a spacer 46 composedof a dielectric substance is inserted between the plate conductor 31 andthe strip conductor 39.

In the fifth embodiment, by using the spacer 46, the interval betweenthe plate conductor 31 and the strip conductor 39 can be accuratelydetermined, and the plate conductor 31 can be stably supported. Further,by changing the dielectric constant of the dielectric substance used, acoupling amount by the feeding can be controlled.

Further, in the above-described fifth embodiment, the feeding shown inthe first and third embodiments can be applied, and thus, by similarlyoperating, the same effect can be obtained.

In the fifth embodiment, although the examples of the plate conductor 31having the approximately rectangular form and the strip conductor 39having the approximately rectangular form as the third conductor plateare shown, these are illustrative only and hence this embodiment is notrestricted to the form shown in FIG. 6.

Further, in the drawing of the fifth embodiment, although the case thatthe longitudinal direction of the strip conductor 39 is coincident withthe longitudinal direction of the plate conductor 31 is exemplified,another arrangement relationship of the strip conductor 39 with respectto the plate conductor 31 other than the above-described can be applied,and, when the arrangement relationship between these members is changed,it is considered that the contribution way of the electric fieldcoupling and the magnetic field coupling can be changed. However, it isconsidered that in case of the feeding on the open end side of the plateconductor 31, the more effective feeding can be performed.

As specifically described in the first to the fifth embodiments, in theantenna device according to the present invention, the non-contactfeeding can be carried out to the antenna from the feeding line.Further, by controlling the coupling amount of the electric field ormagnetic field coupling, the impedance matching between the feeding lineand the antenna can be obtained, and hence an antenna device with aneasy feeding can be obtained.

On the other hand, in a usual antenna device, in order to receive ortransmit only an electric wave of a necessary frequency band, a bandpass filter for passing only a wave of a transmission and receivingfrequency band is provided. That is, by passing only the wave of thetransmission and receiving frequency band, a wave of an unwantedfrequency band can be stopped by the band pass filter. Hence, anunwanted wave outside the receiving frequency band can not enter into areceiver, and only the wave of the transmission frequency band can beemitted from the antenna.

An antenna device according to the present invention also requires aband pass filter. However, in the antenna device according to thepresent invention, since the non-contact feeding from the feeding lineto the antenna is carried out, the effects such as an easy feeding andan easy impedance matching between the feeding line and the antenna canbe obtained, and it is necessary to provide the band pass filter withoutnullifying these beneficial effects.

However, in order to prevent the nullifying of the effects obtained inthe antenna device according to the present invention, it isinsufficient to use a filter of a conventional antenna device requiringa connection cable and connectors.

In an antenna device according to the present invention, a particularfilter is used, as hereinafter described. One embodiment of an antennadevice using a suitable filter according to the present invention willnow be described in connection with the drawings.

FIG. 7 is a block diagram showing a structure of an antenna deviceaccording to the present invention, and this antenna device is providedwith a proper filter for the embodiments.

As shown in FIG. 7, an antenna 45 and resonators 62 are mutuallyconnected by coupling means 47 and are integrated thereby. In FIG. 7,Z_(L) represents a radiation impedance.

FIG. 8 is a constructive view showing a structure of the sixthembodiment of an antenna device according to the present invention.

In the sixth embodiment, as a distinctive feature, a resonant element 54of an inverted F antenna 61 and resonators 62 constitute a band passfilter. Also, the resonant element 54 and the resonators 62 constitutingthe distinctive band pass filter in the sixth embodiment are connectedto each other by the coupling means 47.

The resonators 62 are comprised of an external conductor 51, internalconductors 52 and a dielectric block 55. The internal conductors 52 arearranged in parallel within the dielectric block 55. One set of ends ofthe internal conductors 52 on the same side are short-circuit ends, andthe other ends of the same are open ends. The external conductor 51covers all surfaces or sides of the dielectric block 55 except one sideof the open ends of the internal conductors 52, and one wide widthsurface is tightly contacted with a earth plate 53.

Each coupling means 47, between the adjacent two of the resonators 62,is performed by the electro-magnetic coupling. And the coupling means47, between the resonant element 54 and the resonator 62 located at oneend, is composed of a capacitor 58 and a coupling conductor. Oneelectrode of the capacitor 58 is connected to the internal conductor 52at one end of the resonator 62, and the other electrode of the capacitor58 is coupled with the resonant element 54 of the inverted F antenna 61via the coupling conductor 59. In this case, P1 represents a terminal.

Further, in FIG. 8, since the earth plate 53 and the resonant element 54of the inverted F antenna 61 are the same components as the groundconductor 32 and the plate conductor 31 of the inverted F antenna shownin the first to fifth embodiments described above, it is apparent forthose skilled in the art that the filter shown in this embodiment can beapplied to the inverted F antenna specifically shown in the first tofifth embodiments.

Now, by considering the above-description, the operation of the sixthembodiment of the antenna device described above will be described.

The resonant element 54 (the plate conductor 31) acts as a 1/4wavelength resonant element with one short-circuit end and the otheropen end at a particular frequency. In this case, the coupling amount ofthe resonators 62 and the inverted F antenna 61 can be controlled by theelectrostatic capacity of the capacitors 58.

Now, assuming that the resonant element 54 (the plate conductor 31) ofthe inverted F antenna 61 and the resonators 62 resonate at the samefrequency f_(o), the mutual coupling amounts between the adjacent two ofthe resonators 62 and between the resonant element 54 (the plateconductor 31) and the resonator 62 are controlled so that the resonantelement 54 (the plate conductor 31) and the three resonators 62 mayconstitute the band pass filter. At this time, the received wave nearthe frequency f_(o) incident to the inverted F antenna 61 passes throughthe resonators 62 to be led to the receiver. On the other hand, anotherwave of a frequency different from the frequency f_(o), i.e. outside thepass band of the band pass filter, is stopped even when it is receivedby the inverted F antenna 61, and can not come into the receiver.Further, relating to the transmission wave, by the same operatingprinciple as the receiving operation, only the transmission wave nearthe frequency f_(o) can be emitted from the inverted F antenna 61.

As described above, in the antenna device shown in FIG. 8, the filterpossesses the function for receiving or transmitting only the wave ofthe necessary frequency band.

At this time, since the inverted F antenna 61 and the resonators 62constitute a four stage band pass filter, the impedance matching in thewide band can be performed, and thus no individual matching portion isrequired to the inverted F antenna 61. Also, since the inverted Fantenna 61 also serves as the resonator of the band pass filter, thenumber of the resonators 62 can be reduced by one stage compared withthe conventional filter. Further, since the whole including the antennaconstitute the multi-stage filter, a good impedance characteristic overa wide band can be obtained.

FIG. 9 is a constructive view showing the seventh embodiment of anantenna device according to the present invention. In FIG. 9, the samenumerals denote the same parts as those of the embodiment shown in FIG.8 and thus the description thereof can be omitted for brevity.

In this embodiment, as a distinctive feature, a circular resonator 65 isused and is adapted to perform a electro-magnetic coupling with acoupling element 67. A circular patch antenna 60 is constituted by anexternal conductor 51, a dielectric block 55 and the circular resonator65. In this case, the circular resonator 65 acts as a 1/2 wavelengthresonant element at a particular frequency. The embodiment shown in FIG.9 has the same operating principle and functions as the firstembodiment. Also, since the circular patch antenna 60 and the resonators62 can be integrally constructed by the dielectric block 55, thefabrication of this antenna device can be readily carried out and theminiaturization of the same can also be made possible.

In the aforementioned embodiments, although three or four resonators 62are used, one to two or more than five resonators 62 can be applied, andthe same operating principle and the effects as those of theabove-described embodiments can be obtained.

Further, in the above-described embodiments, although the inverted Fantenna or the patch antenna is used, a dipole antenna can be also used.

Industrial Applicability

As described above, in an antenna device according to the presentinvention, between a first conductor plate for forming a radiationconductor of an antenna and a second conductor plate for forming aground conductor of the antenna, a third conductor plate connected to afeeder line to cause an electric field or magnetic field couplingbetween the first conductor plate and the third conductor plate isarranged, and thus a non-contact feeding from the feeder line to theantenna can be carried out by the electric field or magnetic fieldcoupling. By varying the interval between the first conductor plate andthe third conductor plate or the dimension of the third conductor plate,the coupling amount is controlled, and thus an impedance matching of thefeeder line and the antenna is obtained. Hence, the arrangementrestriction of the first conductor plate and the feeder line can berelieved, and the antenna device capable of readily carrying out thefeeding can be obtained.

Further, in a filter of an antenna device according to the presentinvention, an antenna constituted by a resonant element such as a dipoleantenna, an inverted F antenna, a patch antenna or the like andresonators are integrated by a coupling means to perform an impedancematching, and the resonant element and the resonators constitute a bandpass filter. Hence, the number of resonators constituting the band passfilter can be reduced by one stage, and a filter·antenna device can beminiaturized with a low loss. Also, no individual matching portion isrequired for the antenna, and a small-sized filter·antenna device can beobtained. Further, by including the antenna, a multi filter can beobtained, and thus a filter·antenna which operates over a wide band canbe obtained.

Accordingly, when such a filter is used for an antenna device, theantenna device capable of performing the impedance matching over thewide band can be obtained.

What is claimed is:
 1. A filter antenna device, comprising:a resonantantenna element; a resonator including a plurality of resonant elements,disposed in parallel and enclosed within a metal conductor; couplingmeans for coupling the antenna element to an output of the resonator,said coupling means performed by an electromagnetic coupling, whereinthrough said coupling, the resonator and antenna element in combinationperform an impedance matching between an input of the resonator, whichis coupled to a feeding line, and the antenna element; and the antennaelement and the resonator thereby comprising a band pass filter, whereinsaid antenna element acts as the resonant element of a last stage insaid band pass filter.
 2. An antenna device, comprising:a firstconductive element; a second conductive element disposed below andsubstantially in parallel with the first conductive element; and N-1resonators, wherein N is an integer greater than 1, disposed inparallel, between the first conductive element and the second conductiveelement whereby the N-1 resonators and the first conductive elementcombine to form an N-stage band pass filter, wherein said firstconductive element acts as a last stage in said N-stage band passfilter.
 3. The antenna device as claimed in claim 2, wherein the firstconductive element operates at a quarter wavelength of a resonatefrequency of the antenna.
 4. The antenna device as claimed in claim 2,wherein the first conductive element is a circular resonator whichoperates at a half wavelength of a resonate frequency of the antenna. 5.The antenna device as claimed in claim 2, further comprising acapacitive element disposed between the first conductive element and oneof the plurality of resonators.
 6. The antenna device as claimed inclaim 2, wherein one end of the plurality of resonators are shortcircuited together and an opposite end of at least one of a plurality ofresonators is an open circuit.
 7. The antenna device as claimed in claim2, wherein the first conductive element comprises any one of a dipoleantenna, an inverted F antenna, and a patch antenna.
 8. The antennadevice as claimed in claim 2, wherein the resonators are coupledtogether by means of electromagnetic coupling.